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No description available.

Two molecular phylogenetic studies were undertaken to examine relationships within Myricaceae. Analyses of DNA sequences of the plastid rbcL gene, trnL-Fregion and nuclear ITS region showed the family to be monophyletic. In all analyses Canacomyrica, a monotypic genus endemic to New Caledonian that bears several distinctive features such as staminodes in the female flowers, fell into a well- supported clade sister to the rest of Myricaceae. Phylogenetic analyses of ITS and trnL-F sequence data, representing all genera and subgeneric groups, were undertaken using maximum parsimony and Bayesian methods. The following relationships were strongly supported: (Canacomyrica (Comptonia (Myrica, Morella))). The clade containing all species formerly considered to comprise Myrica s.l. was split into two strongly supported clades corresponding to Myrica s.s. and Morella; this finding strengthens the argument for recognition of these as separate genera. Within Morella, two clades corresponded to previously recognized subgenera. Molecular dating analyses were performed using Penalized Likelihood. Close correlations between lineage-specific diversification and major orogenic or climatic events were inferred. This study suggests that much of the diversity in Morella arose during the Neogene and seed-dispersal by birds has been a significant factor in determining the modem distribution. A study of the conservation status of Canacomyrica was conducted using field observations and data from herbarium specimens. This species was found to occur in just eleven fragmented localities: six outside protected areas and three threatened by mining or bush fires. IUCN Red List status of Endangered was recommended. The morphology and ecology of Canacomyrica was studied to enhance knowledge of this poorly known species and provide comparative data for use in a study of the morphology of the entire family. A new classification scheme with keys was presented including, for the first time, Canacomyrica. New combinations in Morella were recommended.

Philosophiae Doctor - PhD / Frankia is one of two partners in the globally distributed N2-fixing actinorhizal symbiosis between this filamentous soil-dwelling actinomycete and almost 300 species of host plants from eight diverse angiosperm families. The actinorhizal symbiosis is a major contributor to nitrogen reservoirs in terrestrial ecosystems, and allows actinorhizal plants to perform the role of pioneers in newly formed and nitrogen-poor soils. Frankia are differentiated into four main host-infection groups (1: Alnus/Comptonia/Myrica-infective, 2: Rosaceae/Datisca/Coriaria-infective, 3: Elaeagnaceae/Gymnostoma-infective and 4: Casuarina-infective), and there is a large degree of phylogenetic clustering within these HIGs. Of these host lineages, species from the genus Morella, from the family Myricaceae, are notable as they have the ability to establish effective partnerships with Frankia from more than one host-infection group. Africa houses 16 of the world’s 33 currently accepted Morella species, and Morella is the continents only genus containing endemic actinorhizal species. Despite this, the diversity of Frankia in symbiosis with African Morella has never been explored. To address this lack of knowledge I investigated Frankia in root nodules of six Morella species from the Cape flora of Southern Africa, as well as in rhizosphere soils from selected hosts. Partial nif H gene fragments recovered from 202 root nodules yielded 26 unique sequences, which phylogenetic analysis assigned to Frankia Cluster I (the Alnus host infection group) and Frankia Cluster III (the Elaeagnus host infection group)1. Nineteen nif H sequences were assigned to three sub-clusters within Frankia Cluster III (CC-3, CC-4 and CC-5), and the remaining seven sequences to two sub-clusters within Cluster I (CC-1 and CC-2), one of which (CC-1) is novel to the current study. Identical sequences were recovered from nodules collected at geographically distant locations, suggesting a cosmopolitan distribution within the region for some subgroups from both clusters, but more localized distribution (or tighter host-specificity) for others. Soil pH correlated with strain presence in nodules, with Cluster I sequences being associated with hosts growing in acidic soils exclusively. Furthermore, three Morella species from the Cape flora of southern Africa are promiscuous in their natural habitats, with host infection group influenced by habitat edaphic conditions. In order to explore the correlation between soil characteristics and Frankia presence in nodules, nif H soil libraries were created from selected host rhizospheres. While Cluster III sequences from these libraries corresponded closely to sequences found in nodules from the same sites, the dominant Cape Cluster I group (CC-1) was absent from all six libraries, even when present in nodules recovered from the same soils. Whether this was due to low abundance of -but strong selection for- these strains by hosts under particular conditions, or due to the absence in soil of hyphal forms of these strains could not be determined. Cluster III strains are known to be better able to persist saprophytically than their relatives from other host-infection groups. A second group of Cluster I strains, detected at only one sampling site, was present in that site's corresponding soil library. An Alnus-infective subgroup, cluster AI, which has been detected in soils collected on five continents, was also detected in the of the Cape soil libraries but never in nodules, raising questions as to this group’s ability to persist in soil in the absence of known suitable hosts. Ten Frankia strains representing all three of the numerically dominant subgroups (CC-1, CC-3 and CC-4, found in 186 of 202 root nodules) were isolated from four Morella species. These isolates represent six of the most abundant unique nodular nif H sequences found in the field survey, and display morphological and cultural characteristics typical of Frankia. Phylogenetic analysis confirmed their identity as Frankia, and multilocus analysis revealed that the isolates belong to three genospecies. Two of these genospecies fall into existing groups within the Elaeagnus-infective Cluster III, while the remaining genospecies is a novel addition to the otherwise well-described Alnus-infective Cluster I. Whole genome sequencing of a representative from each of the Cape genospecies allowed for basic annotation and genome descriptions, which agreed in each case with what has been previously found for strains from the Elaeagnus and Alnus host-infection groups, respectively. Similarly, the organization of nitrogenase gene clusters in each of the sequenced strains mirrors that found in other strains from their respective host-infection groups, indicating that this gene cluster is highly conserved in different Frankia lineages. For the first time the diversity of Frankia nodulating endemic African Morella, and present in root-associated soils of these species, has been explored. This is also the first study to report isolation and description of Frankia strains from actinorhizal plants endemic to Africa.